Febrile controls exhibited significantly higher CRP levels (CRP 11.5 mg/l, IQR 8.25–45.75 mg/l) compared to children with FS (CRP 5 mg/l, IQR 0–7 mg/l; p = 0.016) at presentation and were more frequently diagnosed with lower than upper respiratory tract infections (Table 2). This evidence concerns the gene CRP and Recurrent upper respiratory tract infections.